Comparative biochemical characterization of soluble and chitosan immobilized β-galactosidase from Kluyveromyces lactis NRRL Y1564

Non-carrier immobilization of yeast cells by genipin crosslinking for the synthesis of prebiotic galactooligosaccharides from plant-derived galactose

Galactooligosaccharides (GOS), as mimics of human milk oligosaccharides, are important prebiotics for modulating the ecological balance of intestinal microbiota. A novel carrier-free cell immobilization method was established using genipin to cross-link Kluyveromyces lactis CGMCC 2.1494, which produced β-galactosidase, an enzyme essential for GOS synthesis. The resulting immobilized cells were characterized as stable by thermogravimetric analysis and confirmed to be crosslinked through scanning electron microscopy analysis (SEM) and Fourier transform infrared spectroscopy (FTIR). The Km and Vmax values of β-galactosidase in immobilized cells towards o-nitrophenyl β-D-galactoside were determined to be 3.446 mM and 2210 μmol min-1 g-1, respectively. The enzyme in the immobilized showed higher thermal and organic solvent tolerance compared to that in free cells. The immobilized cells were subsequently employed for GOS synthesis using plant-derived galactose as the substrate. The synthetic reaction conditions were optimized through both single-factor experiments and response surface methodology, resulting in a high yield of 49.1 %. Moreover, the immobilized cells showed good reusability and could be reused for at least 20 batches of GOS synthesis, with the enzyme activity remaining above 70 % at 35 °C.

Magnetic CLEAs of β-Galactosidase from Aspergillus oryzae as a Potential Biocatalyst to Produce Tagatose from Lactose

β-galactosidase is an enzyme capable of hydrolysing lactose, used in various branches of industry, mainly the food industry. As the efficient industrial use of enzymes depends on their reuse, it is necessary to find an effective method for immobilisation, maintaining high activity and stability. The present work proposes cross-linked magnetic cross-linked enzyme aggregates (mCLEAs) to prepare heterogeneous biocatalysts of β-galactosidase. Different concentrations of glutaraldehyde (0.6%, 1.0%, 1.5%), used as a cross-linking agent, were studied. The use of dextran-aldehyde as an alternative cross-linking agent was also evaluated. The mCLEAs presented increased recovered activity directly related to the concentration of glutaraldehyde. Modifications to the protocol to prepare mCLEAs with glutaraldehyde, adding a competitive inhibitor or polymer coating, have not been effective in increasing the recovered activity of the heterogeneous biocatalysts or its thermal stability. The biocatalyst prepared using dextran-aldehyde presented 73.6% recovered activity, aside from substrate affinity equivalent to the free enzyme. The thermal stability at 60 °C was higher for the biocatalyst prepared with glutaraldehyde (mCLEA-GLU-1.5) than the one produced with dextran-aldehyde (mCLEA-DEX), and the opposite happened at 50 °C. Results obtained for lactose hydrolysis, the use of its product to produce a rare sugar (D-tagatose) and operational and storage stability indicate that heterogeneous biocatalysts have adequate characteristics for industrial use.

β-Galactosidase from Kluyveromyces lactis: Characterization, production, immobilization and applications - A review

A review on the enzyme β-galactosidase from Kluyveromyces lactis is presented, from the perspective of its structure and mechanisms of action, the main catalyzed reactions, the key factors influencing its activity, and selectivity, as well as the main techniques used for improving the biocatalyst functionality. Particular attention was given to the discussion of hydrolysis, transglycosylation, and galactosylation reactions, which are commonly mediated by this enzyme. In addition, the products generated from these processes were highlighted. Finally, biocatalyst improvement techniques are also discussed, such as enzyme immobilization and protein engineering. On these topics, the most recent immobilization strategies are presented, emphasizing processes that not only allow the recovery of the biocatalyst but also deliver enzymes that show better resistance to high temperatures, chemicals, and inhibitors. In addition, genetic engineering techniques to improve the catalytic properties of the β-galactosidases were reported. This review gathers information to allow the development of biocatalysts based on the β-galactosidase enzyme from K. lactis, aiming to improve existing bioprocesses or develop new ones.

The β-galactosidase immobilization protocol determines its performance as catalysts in the kinetically controlled synthesis of lactulose

In this paper, 3 different biocatalysts of β-galactosidase from Kluyveromyces lactis have been prepared by immobilization in chitosan activated with glutaraldehyde (Chi_Glu_Gal), glyoxyl agarose (Aga_Gly_Gal) and agarose coated with polyethylenimine (Aga_PEI_Gal). These biocatalysts have been used to catalyze the synthesis of lactulose from lactose and fructose. Aga-PEI-Gal only produces lactulose at 50 °C, and not at 25 or 37 °C, Aga_Gly_Gal was unable to produce lactulose at any of the assayed temperatures while Chi_Glu_Gal produced lactulose at all assayed temperatures, although a lower yield was obtained at 25 or 37 °C. The pre-incubation of this biocatalyst at 50 °C permitted to obtain similar yields at 25 or 37 °C than at 50 °C. The use of milk whey instead of pure lactose and fructose produced an improvement in the yields using Aga_PEI_Gal and a decrease using Chi_Glu_Gal. The operational stability also depends on the reaction medium and of biocatalyst. This study reveals how enzyme immobilization may greatly alter the performance of β-galactosidase in a kinetically controlled manner, and how medium composition influences this performance due to the kinetic properties of β-galactosidase.

Alternative Heterologous Expression of L-Arabinose Isomerase from Enterococcus faecium DBFIQ E36 By Residual Whey Lactose Induction

This study reports an alternative strategy for the expression of a recombinant L-AI from Enterococcus faecium DBFIQ E36 by auto-induction using glucose and glycerol as carbon sources and residual whey lactose as inducer agent. Commercial lactose and isopropyl β-D-1-thiogalactopyranoside (IPTG) were also evaluated as inducers for comparison of enzyme expression levels. The enzymatic extracts were purified by affinity chromatography, characterized, and applied in the bioconversion of D-galactose into D-tagatose. L-AI presented a catalytic activity of 1.67 ± 0.14, 1.52 ± 0.01, and 0.7 ± 0.04 U/mL, when expressed using commercial lactose, lactose from whey, and IPTG, respectively. Higher activities could be obtained by changing the protocol of enzyme extraction and, for instance, the enzymatic extract produced with whey presented a catalytic activity of 3.8 U/mL. The specific activity of the enzyme extracts produced using lactose (commercial or residual whey) after enzyme purification was also higher when compared to the enzyme expressed with IPTG. Best results were achieved when enzyme expression was conducted using 4 g/L of residual whey lactose for 11 h. These results proved the efficacy of an alternative and economic protocol for the effective expression of a recombinant L-AI aiming its high-scale production.

β-galactosidase from Kluyveromyces lactis in genipin-activated chitosan: An investigation on immobilization, stability, and application in diluted UHT milk

The objective of this research was to evaluate the immobilization of the enzyme β-galactosidase in a genipin-activated chitosan support. The influence of the number of spheres and substrate concentration on immobilization yield (IY) and enzyme activity (EA) was analyzed using experimental design. Thermal, operational and storage stabilities were assessed, and the enzymatic derivatives were characterized by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The TGA showed that the enzymatic derivatives kept their thermal behavior, and the SEM images revealed smooth surfaces in all the spheres. The optimized conditions for the immobilization process were 4.57 mg·mL^-1 of spheres and a substrate concentration of 10 mM (IY = 84.13%; EA = 24.97 U·g^-1). Thermal stability was enhanced at 10 and 37 °C, enabling four successive cycles of lactose hydrolysis in diluted UHT milk. Therefore, the immobilized enzyme in genipin-activated chitosan has potential for lactose hydrolysis and applications in the food industry.

Lactose hydrolysis using β-galactosidase from Kluyveromyces lactis immobilized with sodium alginate for potential industrial applications

The present study aimed to evaluate the lactose hydrolysis conditions from "coalho" cheese whey using β-galactosidase (β-gal) produced by Kluyveromyces lactis immobilized with sodium alginate. Three sodium alginate-based immobilization systems were evaluated (0.5, 0.7, and 1% w/v) for maximizing the immobilization yield (Y), efficiency (EM), and recovered activity (ar). The lactose hydrolysis capacity of the immobilized form of β-gal was determined, and simulated environments were used to assess the preservation of the immobilized enzyme in the gastrointestinal tract. The results showed that β-gal immobilization with 1% (w/v) sodium alginate presented the best results (EM of 66%, Y of 41%, and ar of 65%). The immobilization system maintained the highest pH stability in the range between 5.0 and 7.0, with the highest relative activity obtained under pH 5 conditions. The temperature stability was also favored by immobilization at 50 °C for 30 min was obtained a relative activity of 180.0 ± 1.37%. In 6 h, the immobilized β-gal was able to hydrolyze 46% of the initial lactose content. For the gastrointestinal simulations, around 40% of the activity was preserved after 2 h. Overall, the results described here are promising for the industrial applications of β-galactosidase from K. lactis.

Recent advances in β-galactosidase and fructosyltransferase immobilization technology

The highly demanding conditions of industrial processes may lower the stability and affect the activity of enzymes used as biocatalysts. Enzyme immobilization emerged as an approach to promote stabilization and easy removal of enzymes for their reusability. The aim of this review is to go through the principal immobilization strategies addressed to achieve optimal industrial processes with special care on those reported for two types of enzymes: β-galactosidases and fructosyltransferases. The main methods used to immobilize these two enzymes are adsorption, entrapment, covalent coupling and cross-linking or aggregation (no support is used), all of them having pros and cons. Regarding the support, it should be cost-effective, assure the reusability and an easy recovery of the enzyme, increasing its stability and durability. The discussion provided showed that the type of enzyme, its origin, its purity, together with the type of immobilization method and the support will affect the performance during the enzymatic synthesis. Enzymes' immobilization involves interdisciplinary knowledge including enzymology, nanotechnology, molecular dynamics, cellular physiology and process design. The increasing availability of facilities has opened a variety of possibilities to define strategies to optimize the activity and re-usability of β-galactosidases and fructosyltransferases, but there is still great place for innovative developments.

Potential of "coalho" cheese whey as lactose source for β-galactosidase and ethanol co-production by Kluyveromyces spp. yeasts

The present study evaluated the co-production of β-galactosidase and ethanol by Kluyveromyces marxianus ATCC 36907 and Kluyveromyces lactis NRRL Y-8279 using as carbon source the lactose found on "coalho" cheese whey. Cheese whey was subjected to partial deproteinization, and physicochemical parameters were assessed. Cultivations were carried out in an shaker to evaluate two carbon/nitrogen (C:N) ratios. The best C:N ratio (1.5:1) was carried to 1.5-L bioreactor cultivation in order to increase co-production yields. The stability of β-galactosidase was assessed against different temperatures and pH, and in the presence of metal ions. Concerning the co-production of β-galactosidase and ethanol, K. lactis proved to be more efficient in both the C:N ratios, reaching 21.09 U·mL^-1 of activity and 7.10 g·L^-1 of ethanol in 16 h. This study describes the development of a viable and value-adding biotechnological process using a regional cheese by-product from Northeast Brazil for co-production of biomolecules of industrial interest.

Stability evaluation of 6-phosphogluconate dehydrogenase immobilized on amino-functionalized magnetic nanoparticles

In this study, 6-phosphogluconate dehydrogenase was covalently immobilized onto the N-2-aminoethyl-3-aminopropyltriethoxysilane (APTES) modified core-shell Fe₃O₄@SiO₂ magnetic nanoparticles (ASMNPs) using glutaraldehyde (GA). Immobilization of 6PGDH on ASMNPs was confirmed using fourier transform-infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) analysis. The NADP⁺ conversion ratio, the reusability, thermal, and storage stability of the immobilized 6PGDH were determined and compared with those of the free enzyme. The maximum retention of enzyme activity reached to 96% when the enzyme was immobilized on ASMNPs activated with monomer form of GA. Although the thermal stability of free and immobilized enzymes was similar, at 30 °C, the immobilized 6PGDH showed the improved thermal stability at 40 °C and 50 °C compared with free 6PGDH. While the free 6PGDH only converted 33% of NADP⁺ in reaction medium upon 480 s, the immobilized 6PGDH performed 56% conversion of NADP⁺ at same time. The immobilized 6PGDH retained 62% of its initial activity up to the fifth cycle and 35% of its initial activity after 22 days of storage at 4 °C.

Engineering the l-Arabinose Isomerase from Enterococcus Faecium for d-Tagatose Synthesis

l-Arabinose isomerase (EC 5.3.1.4) (l-AI) from Enterococcus faecium DBFIQ E36 was overproduced in Escherichia coli by designing a codon-optimized synthetic araA gene. Using this optimized gene, two N- and C-terminal His-tagged-l-AI proteins were produced. The cloning of the two chimeric genes into regulated expression vectors resulted in the production of high amounts of recombinant N-His-l-AI and C-His-l-AI in soluble and active forms. Both His-tagged enzymes were purified in a single step through metal-affinity chromatography and showed different kinetic and structural characteristics. Analytical ultracentrifugation revealed that C-His-l-AI was preferentially hexameric in solution, whereas N-His-l-AI was mainly monomeric. The specific activity of the N-His-l-AI at acidic pH was higher than that of C-His-l-AI and showed a maximum bioconversion yield of 26% at 50 °C for d-tagatose biosynthesis, with Km and Vmax parameters of 252 mM and 0.092 U mg^-1, respectively. However, C-His-l-AI was more active and stable at alkaline pH than N-His-l-AI. N-His-l-AI follows a Michaelis-Menten kinetic, whereas C-His-l-AI fitted to a sigmoidal saturation curve.